The present invention relates to a process for the preparation of a nano sized colloidal metal particle. More particularly, the present invention relates to a process for the preparation of a nano sized colloidal metal particle using naturally occurring bio-materials.
Nanoparticles are extremely important materials with utility in different areas ranging from nano-technology, non-linear optics, diode lasers, smart sensors, markers in drugs, gene sequencing to catalysts. In the art, nano materials are obtained by different chemical and physical methods. Chemical methods for the preparation of nano-materials include borohydride and citrate reduction methods for the preparation of colloidal metal such a gold and silver [Handley D. A., Colloidal Gold: Principles, Methods and Applications, Hayat M. A.ed., Academic Press, San Diego Calif., 1989, Vol. 1, Chapter 2]. Physical methods for the preparation of nano materials include vapour deposition, lithographic processes and molecular beam epitaxy (MBE). Reduction of metal ions by radiolysis is also frequently used for the preparation of nano-sized metal particles.
However, the prior art methods described above suffer from several drawbacks. The chemical methods are environmentally hazardous and result in quick agglomeration of nano-particles leading to big particles of poor monodispersity. While specific capping agents are used in some of the above methods to restrict the size of the colloidal metal particles and to stabilise the particle size distribution, use of such capping agents makes the system complicated and userxe2x80x94unfriendly. The radiolysis method is quite complicated and gamma ray sources are not readily available.
Accordingly, it is important to develop processes for the preparation of nano-particles which overcome the drawbacks enumerated above.
The main object of the invention is to provide a process for the preparation of nano sized colloidal metal particles that is environmentally friendly.
It is another object of the invention to provide a process for the preparation of nano-sized colloidal metal particles that is user friendly.
It is a further object of the invention to provide a process for the preparation of nano-sized colloidal metal particles that results in colloidal metal particles with improved stability in aqueous solution.
It is another object of the invention to provide an economic and efficient process for the preparation of nano-sized colloidal metal particles.
These and other objects of the invention are achieved by the process of the invention which uses a biological method for the preparation of nano-sized colloidal metal particles.
Accordingly the present invention provides a process for the preparation of nano-sized colloidal metal particles, said process comprising treating wet fungus or fungus extract with a metal ion solution at a temperature in the range of 15 to 40xc2x0 C. for a time period ranging between 2 to 120 hours, separating the biomass to obtain the nano-sized colloidal metal particles.
In one embodiment of the invention, the concentration of the metal ions in the solution ranges from 0.01 to 0.2 g per gram of the wet fungus mycelial mass.
In another embodiment of the invention, the metal ion solution is prepared by dissolving the desired metal salt or acid in water.
In yet another embodiment of the invention, the metal ions comprise metal from Group IB to VIIIB of the periodic table.
In a further embodiment of the invention, the metal ions are selected from the group consisting of Au, Ag, Pd, Pt, Ni, Rh and Ru.
In another embodiment of the invention, the metal salt used for the preparation of the metal ion solution is selected from the group consisting of halide, carbonate and nitrate.
In a further embodiment of the invention, the concentration of the metal ion per gram of the wet fungus or fungus extract is in the range of 10 to 200 mg.
In a further embodiment of the invention, the concentration of the metal ion per gram of the wet fungus or fungus extract is in the range of 10 to 100 mg.
In a further embodiment of the invention, the concentration of the metal ion per gram of the wet fungus or fungus extract is in the range of 25 to 100 mg.
In another embodiment of the invention, the ratio of water to wet fungus or fungus extract ranges between 1:100 (w/w).
In another embodiment of the invention, the fungus used is selected from different species of Fusarium oxysporum. 
In a further embodiment of the invention, the fungus is used in the form of a whole cell wet solid mass or a fungus extract.
In another embodiment of the invention, the reaction of the fungus and the metal ion source is carried out in water.
In another embodiment of the invention, the temperature for incubation is in the range of 23-33xc2x0 C., preferably 25-29xc2x0 C.
The process of the invention is described hereinbelow with reference to the following examples, which are illustrative and should not be construed as limiting the scope of the invention.